E2B API keys

• Provider documentation e2b-dev/infra keys: ApiKeyPrefix = "e2b_", keyLength = 20 random bytes, hex.EncodeToString (re-checked 2026-09-28) · observed 2026-09-28 · provider code (ruling R1): e2b_ + exactly 40 lowercase hex (20 random bytes, Go hex encoding), 44 in all, no separator or checksum; the local-dev seed test asserts len(prefix) + 2*20
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Arrival evidence (#434, product redact-secret#905; #860 handoff e2b.md, READY). T1 under ruling R1 on every fact: the provider's generator draws 20 random bytes and hex-encodes them after the e2b_ prefix, and its seed test asserts the 44-byte total; the docs name E2B_API_KEY and show e2b_… placeholders. Without the prefix the body is SHA-1 shaped, so the prefix is load-bearing. Excluded: the retired sk_e2b_ user access token (generation stopped 2026-07-01, tokens stopped working 2026-08-01) is a twin because it is another credential class, uppercase-hex bodies (accepted by the verifier but never issued), 64-hex sandbox tokens (not lexically attributable) and e2b_ package names. Neither pinned peer has an E2B rule. Graduated to a registry detector at the 1127bf9 re-pin (redact-secret PR #938).